摘要: A constellation of intrinsic and extrinsic cellular mechanisms regulates the balance self-renewal differentiation in all stem cells. Stem cells, their progeny, elements microenvironment make up an anatomical structure that coordinates normal homeostatic production functional mature Here we discuss cell niche concept, highlight recent progress, identify important unanswered questions. We focus on three mammalian systems where large numbers cells must be continuously produced throughout adult life: intestinal epithelium, epidermal structures, bone marrow.